With the recent trend toward miniaturization and increased density in electronic devices, there is an increasing demand for photosensitive dry films used for manufacturing LSI and the like. For example, a photosensitive dry film is adhered to the surface of a semiconductor wafer or the like, the photosensitive dry film is subjected to selective exposure with radiation such as light or electron beams, and development processing is performed to form a pattern, then pressure bonding is performed with a transparent substrate (for example, a glass substrate) or the like, and thus it is possible to use the photosensitive dry film as a spacer between a semiconductor wafer and a transparent substrate (refer to, for example, PTL 1).
The photosensitive resin layer of the photosensitive dry film includes a photosensitive material, and is required to be patternable by a photolithography method and also to be able to retain a shape as a spacer or the like. In addition, since pressure bonding is carried out with a transparent substrate after exposure and development, it is also required to have excellent adhesion after patterning, in addition to developability and resolution.
In the related art, as a negative photosensitive composition used for a photosensitive dry film, compositions containing a base material component formed of a novolac resin and an acid generator component such as diazonaphthoquinone have been used. However, since diazonaphthoquinone-based photoacid generators exhibit absorption with respect to the wavelength of light used for exposure, there are problems in that the light intensity differs during the exposure between the upper portion and the lower portion (in the vicinity of the interface with the substrate) of the thick film resist film and the shape of the obtained pattern does not become a desired shape such as a rectangle.
On the other hand, in recent years, as a negative photosensitive composition for a thick film resist or a photosensitive dry film, a composition containing a base material component containing an epoxy group and a cationic polymerization initiator is also used. As the cationic polymerization initiator, a fluorinated antimony-based cationic polymerization initiator having high sensitivity to light (for example, a polymerization initiator having SbF6− in the anion moiety) is widely used.
However, antimony (Sb) is an element for which there are concerns about influence on the environment, human carcinogenicity, and influence on animals and plants, and many antimony compounds including the antimony element are designated as harmful substances. Therefore, in the case where an antimony-based cationic polymerization initiator is used, careful attention must be paid during transportation, storage, disposal, and the like. From such a viewpoint, a negative photosensitive composition using a non-antimony-based cationic polymerization initiator has also recently been proposed (refer to, for example, PTLs 2 and 3).
In addition, a technique (pattern forming technique) of forming a fine pattern on a substrate or the like and processing the lower layer of the pattern by performing etching using this pattern as a mask is widely adopted in the manufacturing of semiconductor elements and liquid crystal display elements. The fine pattern is usually made of an organic material and is formed by a technique such as a lithography method or a nanoimprinting method.
For example, in the lithography method, a step in which a photosensitive film (resist film) is formed on a support such as a substrate by using a photosensitive material (resist material) including a base material component such as a resin, selective exposure with radiation such as light or electron beams is performed on the resist film, and developing treatment is performed to form a pattern of a predetermined shape. As necessary, a step of processing the substrate or the like by etching or plating is performed by using the pattern as a mask to manufacture a semiconductor element or the like. Resist materials are classified into positive and negative materials, and a resist material whose solubility in a developing solution increases in the exposed area is a positive type and a resist material whose solubility in a developing solution decreases in the exposed area is a negative type.
In recent years, there has been an increasing demand for a photosensitive composition (resist composition for a thick film) capable of forming a resist film with a high film thickness (refer to PTL 2 and the like). The resist composition for a thick film is used, for example, in the formation of bumps and metal posts through a plating step. For example, a thick film resist layer having a film thickness of approximately 20 μm is formed on a support and exposed and developed via a predetermined mask pattern to form a resist pattern in which portions where a bump or a metal post is to be formed are selectively removed (delaminated). It is possible to form a bump or a metal post by embedding a conductor such as copper in the removed portion (non-resist portion) through plating and then removing the peripheral resist pattern. As the resist composition for a thick film, the photosensitive composition similar tos the negative photosensitive composition used for the photosensitive dry film or the like is used.